Process for the treatment of a pigment suspended in water and method of manufacturing paper

Abstract

PCT No. PCT/DE91/00376 Sec. 371 Date Jan. 6, 1992 Sec. 102(e) Date Jan. 6, 1992 PCT Filed May 8, 1991 PCT Pub. No. WO91/18148 PCT Pub. Date Nov. 28, 1991.Pigments for the papermaking industry, in particular kaolin, are treated with a high molecular polymerizate that is solvated by means of carboxylate groups and belongs to an ethylenically unsaturated, radically polymerizable carboxylic acid as the binder. By gradually adding an acidifying agent the binder is coacervated and totally precipitated on the pigment. It is important that the quantity of the acidifying agent is limited in such a manner that the pigment retains a negative surface charge and the coacervate still contains water. With the pigment treated thus printing papers with increased pigment content and/or increased breaking strength can be manufactured.

What is claimed as new and desired to be secured by Letters Patent of the United States is: 
     
       1. A process for the treatment of a pigment, suspended in water, with an aqueous binder through precipitation of the binder on the pigment, consisting essentially of gradually adding an acidifying agent to a dissolved binder, the binder being a high molecular polymerizate of an ethylenically unsaturated, radically polymerizable carboxylic acid that is solvated by means of carboxylate groups, avoiding local over-acidification, until the binder coacervates and the coacervate precipitates on a suspended pigment, wherein the quantity of the acidifying agent is limited in such a manner that the pigment retains a negative charge. 
     
     
       2. A process for manufacturing pigment-containing paper through sheet formation from an aqueous stock, wherein said stock contains a pigment treated according to claim 1. 
     
     
       3. A process according to claims 1 or 2, wherein kaolin, calcium sulfate, talcum or titanium dioxide is added as the pigment. 
     
     
       4. A process according to claims 1 or 2, wherein a polymerizate having a molecular weight Mm>20,000 is added as the binder. 
     
     
       5. A process according to claim 4, wherein a polymerizate having a molecular weight Mm>50,000 is added as the binder. 
     
     
       6. A process according to claim 4, wherein a polymerizate containing 6 to 80 wt. % of an ethylenically unsaturated, radically polymerizable carboxylic acid selected from the group consisting of acrylic acid, methacrylic acid, and maleaic acid is added as the binder. 
     
     
       7. A process according to claim 6, wherein the polymerizate contains 10-80 wt. % of said ethylenically unsaturated, radically polymerizable carboxylic acid. 
     
     
       8. A process according to claims 1 or 2, wherein an acid reacting salt of a polyvalent metal cation is added as the acidifying agent. 
     
     
       9. A process according to claim 8, wherein aluminum sulfate is added. 
     
     
       10. An aqueous suspension of a pigment for the paper making industry wherein the treated pigment is made by a process according to claim 1. 
     
     
       11. An aqueous suspension according to claim 10, wherein the aqueous phase has less than 5 wt. % of the binder. 
     
     
       12. An aqueous suspension as claimed in claim 11, wherein the content of the binder in the aqueous phase amounts to no more than 10 wt. %, based on a total binder content of the suspension, following high shear treatment of 3 minutes by means of a high speed agitator at 4,000 rpm.